We [Christians] agree that Christ is the ultimate authority. But who is the visible (i.e. concrete, tangible) authority over the Church between the time of Christ's ascension and the time of His return? Or did Christ go to heaven and leave no one in charge?
It seems to me, from what I gather from your comments, that you think Christ left no one in charge, like sheep without a shepherd.
The sinners in the Church are indeed a shame to the Church. We are called to be a holy body, "unam, sanctam, catholicam et apostolicam ecclesiam". So, whenever leaders in the Church fail to live holy lives, it tarnishes the bride of Christ who is to be spotless. But, if you studied the Donatist heresy, or if you have read about Eli in the Old Testament, or Christ's comment (in the New Testament) about the Pharisees sitting in the seat of Moses, then you will understand that the authority in the Church does not de jure lose its authority on account of its sinfulness. Neither the efficacy of the sacraments administered by such individuals, nor their ordination itself, is revoked by their sins per se. For, the "gifts and calling are irrevocable", as the Scripture teaches. We pray for the purification of Christ's Church, and for her holiness, and for her leaders. And we work to purify ourselves, and our families. But we do not reject the Church, or reject her rightful authorities, on account of their failings, because she remains the Church, and her leaders retain their appointed authority, in spite of their failings.
-A8